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Answering the cost question
The need to maintain an identical secondary storage array is a major problem for storage managers wanting to introduce replication. This approach presents a major expense that may be difficult to justify if the equipment is intended to just sit and wait for a disaster.

In a recent survey of storage managers, StorageTek, of Louisville, CO, found that just 9.4% were mirroring all their data; 37.7% mirrored critical systems; 35.8% mirrored some critical systems and 17.0% weren't mirroring data at all. When asked why they didn't mirror more systems, 83.3% of respondents named the cost of storage as an inhibitor to their fully mirroring data volumes, while 53.8% cited implementation costs as a culprit.

Clearly, a better value proposition will increase the chance of getting funding. If you can plan on using some of the backup data center's capacity to receive and process snapshots--particularly if those snapshots are going to return business value by being fed into data mining applications--the cost can be spread over several important applications.

In this model, the disaster recovery (DR) site becomes not just a big warehouse of idle disks, but a secondary data center where storage of snapshots allows analytical applications to conduct backup and detailed analysis of point-in-time data copies. Recruiting all this extra computing capacity to the cause makes a DR

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investment a little more palatable.

"We've been seeing people saving millions of dollars over a traditional hardware-based approach," says Fairbanks. "If you deploy replication at a disaster recovery location, [the location] serves two functions. That makes it much easier to justify the cost as opposed to having a completely dark data center that's not normally used."

As the current uncertain political climate forces companies to assess and reassess their disaster recovery plans, the need to physically separate copies of data is becoming an issue. However, stubborn distance limitations--and the high cost of the fiber that gets around them--have hindered implementation of synchronous replication across long distances. Instead, more distance-tolerant asynchronous replication--embodied in standalone software solutions from various vendors--is proving to be a much better answer. (For more information on the pros and cons of synchronous and asynchronous replication, see Marc Farley's "Cost-effective business continuity")

More bandwidth means faster replication but, of course, costs more. "We can calculate [usage] and build a pipe that allows us to meet RTOs with a master file that drains to a slave at a speed that guarantees we have no more than an hour, for example, in the pipe at a time," says BlueStar's Augustadt, who says customers typically budget for 80% utilization of their replication links. "Bandwidth determines how fast the log can drain, not how fast you write to it."

In some cases, companies assume that if they have a big database to replicate, they need a fat bandwidth pipe. That's a misnomer: Replication should ideally be performing delta updates, and therefore transferring just a small subset of the entire database.

Most companies focus on optimizing their replication rather than throwing bandwidth at the problem, says Kelly Polanski, vice president of application availability marketing with Legato Systems. "It's very rare that we find companies capable of investing in lots of bandwidth," she says. "That means efficient use of the network--throttling, scheduling so that the network can be shared with WAN usage--is very instrumental in getting a disaster recovery plan in place. Replication provides a way to get data offsite as fast as you can."

Getting data out the door
A high-speed metropolitan connection was just the ticket for America West, America's eighth-largest airline, which is currently setting up a data replication strategy that will improve its business continuity planning.

With some 6TB of EMC Symmetrix storage in place, America West has long relied on EMC's TimeFinder snapshotting tool to generate two hourly snapshots of its Systems Operations and Control (SOC) center, a Phoenix facility that uses custom applications to manage myriad details of every flight.

In its current configuration, the snapshots are copied from one Symmetrix volume to another. A backup server can be booted from the snapshots if necessary. "This is a key component of our business continuity plan," says Joe Beery, senior VP and CIO of American West. "These systems drive the daily operation of the airline, and they're what we consider to be our mission-critical applications."

As the company's recent SAN investment takes hold, its replication is being shifted onto four T1 lines that link the SOC with a secondary data center 6.5 miles away. Other types of data, including data from the airline's Unisys mainframe, will eventually be replicated as well by using an Inrange Technologies ESCON interface that moves the mainframe data over the T1 lines.

Snapshot and replication tools have become important allies in the fight to ensure business continuity. By mapping out business processes to identify which applications need to be fully replicated and which can be backed up less frequently, it's possible to bring a high level of redundancy to key applications at a manageable cost--and then expand the scope of data protection as disk space and corporate priorities allow.

Remember, however, that replication only works well if you have tried-and-true procedures for failing over your primary data center to the secondary site--and back again.

"It's very easy to use this stuff wrong," says James Staten, director of marketing for networked storage with Sun Microsystems. "The majority of customers think they have a DR plan in place, then realize they've never tested it and don't know for sure that it's going to work."

This was first published in June 2003

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